Base-coats and paints which mainly contain the aromatic epoxy resin can exhibit good qualities of processing, durability and coating properties. Accordingly, they are used often for coating, especially metal. The aromatic epoxy resin itself, however, can not dissolve and disperse into aqueous solution.
On the other hand, usual base-coats and paints for metal are studied further from the view of resources-saving, energy-saving and preventing environmental pollution. There are various suggestions about base-coats and paints which mainly contain the aromatic epoxy resin. For example, the method for dispersing the aromatic epoxy resin with surfactant into water is well known, but such surfactants tend to impart bad effects on storage stability and other properties of base-coats and paints.
Certain self-emulsive aromatic epoxy resin comprising an aromatic epoxy resin that is modified by acrylic system resin with carboxyl group has been suggested. For example, Japanese Patent Application Laid-Open No. 53-14963 and Japanese Patent Application Laid-Open No. 55-9433 have reported that partial reactant with excess carboxyl groups, which are produced from reacting with acrylic resin and aromatic epoxy resin are dispersed stably with ammonia or amine in aqueous medium, namely the esterification. Japanese Patent Application Laid-Open No. 57-105418 and Japanese Patent Application Laid-Open No. 58-198513 have reported that a low molecular compound is produced by that aromatic epoxy resin reacts partially with methacrylic acid, and comprises epoxy group and acryloyl group in a molecule, and the low molecular compound and monomer mixture containing acrylic acid or methacrylic acid are polymerized, namely the modified esterification, namely the modified esterification, and the produced polymer is neutralized with basic compound, and an aqueous dispersion composition is obtained. Also, Japanese Patent Application Laid-Open No. 53-1228 reports that a polymerized epoxy resin is obtained by polymerizing a monomer mixture including a carboxylic monomer with a free-radical generation agent such as a benzoyl peroxide in the presence of an aromatic epoxy resin, namely the graft copolymerization, and the graft-copolymerized epoxy resin is able to be dispersed stably into an aqueous medium containing base.
Self-emulsive-type aromatic epoxy resin obtained by the above-described documents can form a rigid film by itself because it does not contain a surfactant in paints. But the self-emulsive-type aromatic epoxy resin is mixed with an aqueous amino resin which has a good hardening property in order to achieve increased hardening speed practically. By mixing with the amino resin, a hardening speed of film is able to be improved without deterioration of film property to a certain extent. However, if the amount which can get a practically satisfactory hardening speed is mixed, the processing and adhesion properties can deteriorate. Especially, painting inside a can give rise to sanitation problem because low molecular compounds which originate from amino resin are dissolved into contents of the can during heat sterilization.
Also, it has been reported that a phenol resin is mixed with the self-emulsive-type aromatic epoxy resin; however, such prior efforts have shown that phenol resin can not contribute to improving hardening speed.
Further, in the case that a base-coat agent for a metal-adhered can by the above-described work is used, sufficient adhesion to metal materials of cans and amide adhesive agents can not be obtained and a suitable base-coat for short-time baking can not be obtained.